This invention relates to electrolytic iron for metallurgical purposes and particularly to a process for producing thick, dense, friable iron deposit chips on the cathode surface by electrolytic deposition which can be easily removed from the cathode and ground to fine mesh size powder. The process of this invention produces improved quality iron chips that substantially improves the yield fraction of very fine powders. Electrolytic iron powders produced by this process are particularly advantageous as being highly pure powders substantially free from metallic and nonmetallic impurities.
Electrolytic iron is produced by electrolytic deposition of metal from an aqueous solution of a suitable iron electrolyte whereby metal is deposited onto a cathode and can be subsequently chipped off or stripped off the cathode and ground into fine powder. To obtain desirable grinding properties of the electrodeposited chips, the chips are preferably dense, brittle deposits and ordinarily require relatively low current density and an electrolyte of relatively low acidity. The electrolytic iron deposited and subsequently utilized for powder metallurgy purposes is quite brittle and has low ductility so that the electrodeposited iron can be readily removed from the cathode and reduced mechanically to a pulverized powder form. The metallographic grains of dense brittle deposits of metal chips ordinarily are irregular or needle-like and are particularly suitable for subsequent mechanical pulverization in one or more steps, such as by grinding in large and small ball mills.
It now has been found that particularly brittle, friable iron chips can be produced in accordance with this invention from aqueous electrolytic baths containing lower concentrations of ferrous sulfate, maintaining a much higher concentration of ammonium sulfate, a lower concentration ratio of ferrous sulfate to ammonium sulfate in the electrolytic bath solution while maintaining pH control of the electrolytic bath. The electrolytic iron deposited onto the cathode is brittle and friable and can be efficiently removed from the cathode. The chips removed can be easily mechanically pulverized into fine powder of less than about -100 mesh (149 microns) wherein the fraction of iron powder below -324 mesh (44 microns) is approximately tripled in comparison to prior known processes.